A 2021 taxonomy update for the family Smacoviridae

2024 Smacoviridae family update: 59 new species in seven genera

Family Smacoviridae (order Cremevirales, class Arfiviricetes, phylum Cressdnaviricota) comprises viruses with small circular genomes of ~2300-3000 nt in length that encode at least two proteins, the rolling-circle replication associated protein (Rep) and the capsid protein (CP). Smacovirids have been discovered in fecal samples of various animals and display remarkable sequence diversity. Here, we provide an overview of the genomic properties of classified smacovirids and report on the latest taxonomy update in the family Smacoviridae. The family has been expanded by 59 new species in the genera Porprismacovirus (n = 25), Inpeasmacovirus (n = 1), Felismacovirus (n = 22), Drosmacovirus (n = 4), Dragsmacovirus (n = 2), Bovismacovirus (n = 4), and Bonzesmacovirus (n = 1) and currently includes 12 genera with 143 species officially recognized by the International Committee on Taxonomy of Viruses (ICTV).

Full-genome sequencing of dozens of new DNA viruses found in Spanish bat feces

Bats are natural hosts of multiple viruses, many of which have clear zoonotic potential. The search for emerging viruses has been aided by the implementation of metagenomic tools, which have also enabled the detection of unprecedented viral diversity. Currently, this search is mainly focused on RNA viruses, which are largely over-represented in databases. To compensate for this research bias, we analyzed fecal samples from 189 Spanish bats belonging to 22 different species using viral metagenomics. This allowed us to identify 52 complete or near-complete viral genomes belonging to the families Adenoviridae, Circoviridae, Genomoviridae, Papillomaviridae, Parvoviridae, Polyomaviridae and Smacoviridae. Of these, 30 could constitute new species, doubling the number of viruses currently described in Europe. These findings open the door to a more thorough analysis of bat DNA viruses and their zoonotic potential.

IMPORTANCE

Metagenomics has become a fundamental tool to characterize the global virosphere, allowing us not only to understand the existing viral diversity and its ecological implications but also to identify new and emerging viruses. RNA viruses have a higher zoonotic potential, but this risk is also present for some DNA virus families. In our study, we analyzed the DNA fraction of fecal samples from 22 Spanish bat species, identifying 52 complete or near-complete genomes of different viral families with zoonotic potential. This doubles the number of genomes currently described in Europe. Metagenomic data often produce partial genomes that can be difficult to analyze. Our work, however, has characterized a large number of complete genomes, thus facilitating their taxonomic classification and enabling different analyses to be carried out to evaluate their zoonotic potential. For example, recombination studies are relevant since this phenomenon could play a major role in cross-species transmission.

Diverse Circular DNA Viral Communities in Blood, Oral, and Fecal Samples of Captive Lemurs

Few studies have addressed viral diversity in lemurs despite their unique evolutionary history on the island of Madagascar and high risk of extinction. Further, while a large number of studies on animal viromes focus on fecal samples, understanding viral diversity across multiple sample types and seasons can reveal complex viral community structures within and across species. Groups of captive lemurs at the Duke Lemur Center (Durham, NC, USA), a conservation and research center, provide an opportunity to build foundational knowledge on lemur-associated viromes. We sampled individuals from seven lemur species, i.e., collared lemur (Eulemur collaris), crowned lemur (Eulemur coronatus), blue-eyed black lemur (Eulemur flavifrons), ring-tailed lemur (Lemur catta), Coquerel's sifaka (Propithecus coquereli), black-and-white ruffed lemur (Varecia variegata variegata), and red ruffed lemur (Varecia rubra), across two lemur families (Lemuridae, Indriidae). Fecal, blood, and saliva samples were collected from Coquerel's sifaka and black-and-white ruffed lemur individuals across two sampling seasons to diversify virome biogeography and temporal sampling. Using viral metagenomic workflows, the complete genomes of anelloviruses (n = 4), cressdnaviruses (n = 47), caudoviruses (n = 15), inoviruses (n = 34), and microviruses (n = 537) were determined from lemur blood, feces, and saliva. Many virus genomes, especially bacteriophages, identified in this study were present across multiple lemur species. Overall, the work presented here uses a viral metagenomics approach to investigate viral communities inhabiting the blood, oral cavity, and feces of healthy captive lemurs.

Metagenomics to Identify Viral Communities Associated with Porcine Respiratory Disease Complex in Tibetan Pigs in the Tibetan Plateau, China

Tibetan pig is a unique pig breed native to the Qinghai-Tibet Plateau. To investigate viral communities associated with porcine respiratory disease complex (PRDC), 167 respiratory samples were collected from Tibetan pigs in the Ganzi Tibetan autonomous prefecture of Sichuan province. Following library construction and Illunima Novaseq sequencing, 18 distinct viruses belonging to 15 viral taxonomic families were identified in Tibetan pigs with PRDC. Among the 18 detected viruses, 3 viruses were associated with PRDC, including porcine circovirus type 2 (PCV-2), Torque teno sus virus (TTSuV), and porcine cytomegalovirus (PCMV). The genomic sequences of two PCV-2 strains, three TTSuV strains, and one novel Porprismacovirus strain were assembled by SOAPdenovo software (v2). Sequence alignment and phylogenetic analysis showed that both PCV-2 strains belonged to PCV-2d, three TTSuVs were classified to TTSuV2a and TTSuV2b genotypes, and the Porprismacovirus strain PPMV-SCgz-2022 showed a close genetic relationship with a virus of human origin. Recombination analysis indicated that PPMV-SCgz-2022 may have originated from recombination events between Human 16,806 × 66-213 strain and Porcine 17,668 × 82-593 strain. Furthermore, the high proportion of single infection or co-infection of PCV2/TTSuV2 provides insight into PRDC infection in Tibetan pigs. This is the first report of the viral communities in PRDC-affected Tibetan pigs in this region, and the results provides reference for the prevention and control of respiratory diseases in these animals.

Metagenomic survey of viral diversity obtained from feces of piglets with diarrhea

Pigs are natural host to various zoonotic pathogens including viruses. In this study, we analyzed the viral communities in the feces of 89 piglets with diarrhea under one month old which were collected from six farms in Jiangsu Province of the Eastern China, using the unbiased virus metagenomic method. A total of 89 libraries were constructed, and 46937894 unique sequence reads were generated by Illumina sequencing. Overall, the family Picornaviridae accounted for the majority of the total reads of putative mammalian viruses. Ten novel virus genomes from different family members were discovered, including Parvoviridae (n = 2), Picobirnaviridae (n = 4) and CRESS DNA viruses (n = 4). A large number of phages were identified, which mainly belonged to the order Caudovirales and the family Microviridae. Moreover, some identified viruses were closely related to viruses found in non-porcine hosts, highlighting the potential for cross-species virus dissemination. This study increased our understanding of the fecal virus communities of diarrhea piglets and provided valuable information for virus monitoring and preventing.

Unveiling CRESS DNA Virus Diversity in Oysters by Virome

Oysters that filter feed can accumulate numerous pathogens, including viruses, which can serve as a valuable viral repository. As oyster farming becomes more prevalent, concerns are mounting about diseases that can harm both cultivated and wild oysters. Unfortunately, there is a lack of research on the viruses and other factors that can cause illness in shellfish. This means that it is harder to find ways to prevent these diseases and protect the oysters. This is part of a previously started project, the Dataset of Oyster Virome, in which we further study 30 almost complete genomes of oyster-associated CRESS DNA viruses. The replication-associated proteins and capsid proteins found in CRESS DNA viruses display varying evolutionary rates and frequently undergo recombination. Additionally, some CRESS DNA viruses have the capability for cross-species transmission. A plethora of unclassified CRESS DNA viruses are detectable in transcriptome libraries, exhibiting higher levels of transcriptional activity than those found in metagenome libraries. The study significantly enhances our understanding of the diversity of oyster-associated CRESS DNA viruses, emphasizing the widespread presence of CRESS DNA viruses in the natural environment and the substantial portion of CRESS DNA viruses that remain unidentified. This study's findings provide a basis for further research on the biological and ecological roles of viruses in oysters and their environment.

The crystal structure of the human smacovirus 1 Rep domain

Replication initiator proteins (Reps) from the HUH endonuclease family process specific single-stranded DNA sequences to initiate rolling-circle replication in viruses. Here, the first crystal structure of the apo state of a Rep domain from the smacovirus family is reported. The structure of the human smacovirus 1 Rep domain was obtained at 1.33 Å resolution and represents an expansion of the HUH endonuclease superfamily, allowing greater diversity in bioconjugation-tag applications.

A compendium of viruses from methanogenic archaea reveals their diversity and adaptations to the gut environment

Methanogenic archaea are major producers of methane, a potent greenhouse gas and biofuel, and are widespread in diverse environments, including the animal gut. The ecophysiology of methanogens is likely impacted by viruses, which remain, however, largely uncharacterized. Here we carried out a global investigation of viruses associated with all current diversity of methanogens by assembling an extensive CRISPR database consisting of 156,000 spacers. We report 282 high-quality (pro)viral and 205 virus-like/plasmid sequences assigned to hosts belonging to ten main orders of methanogenic archaea. Viruses of methanogens can be classified into 87 families, underscoring a still largely undiscovered genetic diversity. Viruses infecting gut-associated archaea provide evidence of convergence in adaptation with viruses infecting gut-associated bacteria. These viruses contain a large repertoire of lysin proteins that cleave archaeal pseudomurein and are enriched in glycan-binding domains (Ig-like/Flg_new) and diversity-generating retroelements. The characterization of this vast repertoire of viruses paves the way towards a better understanding of their role in regulating methanogen communities globally, as well as the development of much-needed genetic tools.

Virome of high-altitude canine digestive tract and genetic characterization of novel viruses potentially threatening human health

The majority of currently emerging infectious illnesses are zoonotic infections, which have caused serious public health and economic implications. The development of viral metagenomics has helped us to explore unknown viruses. We collected 1,970 canine feces from Yushu and Guoluo in the plateau region of China for this study to do a metagenomics analysis of the viral community of the canine digestive tract. Our analysis identified 203 novel viruses, classified into 11 known families and 2 unclassified groups. These viruses include the hepatitis E virus, first identified in dogs, and the astrovirus, coronavirus, polyomavirus, and others. The relationship between the newly identified canine viruses and known viruses was investigated through the use of phylogenetic analysis. Furthermore, we demonstrated the cross-species transmission of viruses and predicted new viruses that may cause diseases in both humans and animals, providing technical support for the prevention and control of diseases caused by environmental pollution viruses. IMPORTANCE Most emerging infectious diseases are due to zoonotic disease agents. Because of their effects on the security of human or animal life, agriculture production, and food safety, zoonotic illnesses and livestock diseases are of worldwide significance. Because dogs are closely related to humans and domestic animals, they serve as one of the important links in the transmission of zoonotic and livestock diseases. Canines can contaminate the environment in which humans live such as water and soil through secretions, potentially altering the human gut microbiota or causing diseases. Our study enriched the viral community in the digestive tract microbiome of dogs and found types of viruses that threaten human health, providing technical support for the prevention and control of early warning of diseases caused by environmental contaminant viruses.

Characterization of Diverse Anelloviruses, Cressdnaviruses, and Bacteriophages in the Human Oral DNA Virome from North Carolina (USA)

The diversity of viruses identified from the various niches of the human oral cavity-from saliva to dental plaques to the surface of the tongue-has accelerated in the age of metagenomics. This rapid expansion demonstrates that our understanding of oral viral diversity is incomplete, with only a few studies utilizing passive drool collection in conjunction with metagenomic sequencing methods. For this pilot study, we obtained 14 samples from healthy staff members working at the Duke Lemur Center (Durham, NC, USA) to determine the viral diversity that can be identified in passive drool samples from humans. The complete genomes of 3 anelloviruses, 9 cressdnaviruses, 4 Caudoviricetes large bacteriophages, 29 microviruses, and 19 inoviruses were identified in this study using high-throughput sequencing and viral metagenomic workflows. The results presented here expand our understanding of the vertebrate-infecting and microbe-infecting viral diversity of the human oral virome in North Carolina (USA).

Searching for a Reliable Viral Indicator of Faecal Pollution in Aquatic Environments

The disposal of sewage in significant quantities poses a health hazard to aquatic ecosystems. These effluents can contain a wide range of pathogens, making faecal contamination a leading source of waterborne diseases around the world. Yet monitoring bacteria or viruses in aquatic environments is time consuming and expensive. The standard indicators of faecal pollution all have limitations, including difficulty in determining the source due to lack of host specificity, poor connection with the presence of non-bacterial pathogens, or low environmental persistence. Innovative monitoring techniques are sorely needed to provide more accurate and targeted solutions. Viruses are a promising alternative to faecal indicator bacteria for monitoring, as they are more persistent in ambient water, more abundant in faeces, and are extremely host-specific. Given the range of viruses found in diverse contexts, it is not easy to find one "ideal" viral indicator of faecal pollution; however, several are of interest. In parallel, the ongoing development of molecular techniques coupled with metagenomics and bioinformatics should enable improved ways to detect faecal contamination using viruses. This review examines the evolution of faecal contamination monitoring with the following aims (i) to identify the characteristics of the main viral indicators of faecal contamination, including human enteric viruses, bacteriophages, CRESS and plant viruses, (ii) to assess how these have been used to monitor water pollution in recent years, (iii) to evaluate the reliability of recent detection methods of such viruses, and (iv) to tentatively determine which viruses may be most effective as markers of faecal pollution.

Naryaviridae, Nenyaviridae, and Vilyaviridae: three new families of single-stranded DNA viruses in the phylum Cressdnaviricota

The phylum Cressdnaviricota includes viruses with circular single-stranded DNA (ssDNA) genomes and icosahedral capsids. These viruses display global environmental distribution and infect diverse eukaryotic hosts, including animals, plants, and fungi. Here, we report on the formal creation of two new orders, Rivendellvirales and Rohanvirales, and three new families, Naryaviridae, Nenyaviridae, and Vilyaviridae, of ssDNA viruses associated with protozoan parasites belonging to the genera Entamoeba and Giardia. We describe a sequence-based taxonomic framework, which was used to classify 60 ssDNA viruses into 12 genera (with 18 species) within the family Vilyaviridae; four genera (with five species) within the family Naryaviridae; and five genera (with six species) within the family Nenyaviridae. We also highlight the challenges associated with the classification of chimeric virus genomes, such as those in the families Naryaviridae and Nenyaviridae, where the replication initiation and capsid protein genes have undergone several independent non-orthologous replacements. The described taxonomic changes have been ratified by the International Committee on Taxonomy of Viruses (ICTV) and expand the phylum Cressdnaviricota to eight orders and 11 families.

Multiple novel smaco-like viruses identified in chicken cloaca swabs

Viral metagenomics has been used in numerous animal virus discoveries. Recently, an unprecedented diversity of CRESS DNA viruses was identified using this method, and this has expanded our understanding of the environmental distribution and host range of CRESS DNA viruses. In this study, using an unbiased viral metagenomics approach, we investigated the fecal virome of chickens collected from two farms of Anhui Province, China. Five novel CRESS DNA viruses were obtained and characterized. The genome of the five viruses is 2,401-2,742 bp in length, containing two ORFs in the same orientation. Phylogenetic analysis indicated that all five viruses have a closer genetic relationship to smacoviruses than to other viruses in the order Cremevirales. Pairwise comparison of Rep amino acid sequences showed that these five viruses had only low amino acid sequence identity (8.9%-30.6%) to members of the family Smacoviridae, and the sequence identity among the five smaco-like viruses and other unclassified smacovirus strains was 70.3-95.8%. These findings broaden our knowledge of the genetic diversity of CRESS DNA viruses and provide a basis for classification of unclassified smacoviruses.

Virome in the cloaca of wild and breeding birds revealed a diversity of significant viruses

BACKGROUND

Wild birds may harbor and transmit viruses that are potentially pathogenic to humans, domestic animals, and other wildlife.

RESULTS

Using the viral metagenomic approach, we investigated the virome of cloacal swab specimens collected from 3182 birds (the majority of them wild species) consisting of > 87 different species in 10 different orders within the Aves classes. The virus diversity in wild birds was higher than that in breeding birds. We acquired 707 viral genomes from 18 defined families and 4 unclassified virus groups, with 265 virus genomes sharing < 60% protein sequence identities with their best matches in GenBank comprising new virus families, genera, or species. RNA viruses containing the conserved RdRp domain with no phylogenetic affinity to currently defined virus families existed in different bird species. Genomes of the astrovirus, picornavirus, coronavirus, calicivirus, parvovirus, circovirus, retrovirus, and adenovirus families which include known avian pathogens were fully characterized. Putative cross-species transmissions were observed with viruses in wild birds showing > 95% amino acid sequence identity to previously reported viruses in domestic poultry. Genomic recombination was observed for some genomes showing discordant phylogenies based on structural and non-structural regions. Mapping the next-generation sequencing (NGS) data respectively against the 707 genomes revealed that these viruses showed distribution pattern differences among birds with different habitats (breeding or wild), orders, and sampling sites but no significant differences between birds with different behavioral features (migratory and resident).

CONCLUSIONS

The existence of a highly diverse virome highlights the challenges in elucidating the evolution, etiology, and ecology of viruses in wild birds. Video Abstract.

Viral Metagenomic Data Analyses of Five New World Bat Species from Argentina: Identification of 35 Novel DNA Viruses

Bats are natural reservoirs of a variety of zoonotic viruses, many of which cause severe human diseases. Characterizing viruses of bats inhabiting different geographical regions is important for understanding their viral diversity and for detecting viral spillovers between animal species. Herein, the diversity of DNA viruses of five arthropodophagous bat species from Argentina was investigated using metagenomics. Fecal samples of 29 individuals from five species (Tadarida brasiliensis, Molossus molossus, Eumops bonariensis, Eumops patagonicus, and Eptesicus diminutus) living at two different geographical locations, were investigated. Enriched viral DNA was sequenced using Illumina MiSeq, and the reads were trimmed and filtered using several bioinformatic approaches. The resulting nucleotide sequences were subjected to viral taxonomic classification. In total, 4,520,370 read pairs were sequestered by sequencing, and 21.1% of them mapped to viral taxa. Circoviridae and Genomoviridae were the most prevalent among vertebrate viral families in all bat species included in this study. Samples from the T. brasiliensis colony exhibited lower viral diversity than samples from other species of New World bats. We characterized 35 complete genome sequences of novel viruses. These findings provide new insights into the global diversity of bat viruses in poorly studied species, contributing to prevention of emerging zoonotic diseases and to conservation policies for endangered species.

Diverse Single-Stranded DNA Viruses Identified in Chicken Buccal Swabs

High-throughput sequencing approaches offer the possibility to better understand the complex microbial communities associated with animals. Viral metagenomics has facilitated the discovery and identification of many known and unknown viruses that inhabit mucosal surfaces of the body and has extended our knowledge related to virus diversity. We used metagenomics sequencing of chicken buccal swab samples and identified various small DNA viruses with circular genome organization. Out of 134 putative circular viral-like circular genome sequences, 70 are cressdnaviruses and 26 are microviruses, whilst the remaining 38 most probably represent sub-genomic molecules. The cressdnaviruses found in this study belong to the Circoviridae, Genomoviridae and Smacoviridae families as well as previously described CRESS1 and naryavirus groups. Among these, genomoviruses and smacoviruses were the most prevalent across the samples. Interestingly, we also identified 26 bacteriophages that belong to the Microviridae family, whose members are known to infect enterobacteria.

Perspective on taxonomic classification of uncultivated viruses

Historically, virus taxonomy has been limited to describing viruses that were readily cultivated in the laboratory or emerging in natural biomes. Metagenomic analyses, single-particle sequencing, and database mining efforts have yielded new sequence data on an astounding number of previously unknown viruses. As metagenomes are relatively free of biases, these data provide an unprecedented insight into the vastness of the virosphere, but to properly value the extent of this diversity it is critical that the viruses are taxonomically classified. Inclusion of uncultivated viruses has already improved the process as well as the understanding of the taxa, viruses, and their evolutionary relationships. The continuous development and testing of computational tools will be required to maintain a dynamic virus taxonomy that can accommodate the new discoveries.